The major aims of this proposal are: 1) to determine the dose-response effects of the stimulant drug methylphenidate (Ritalin) on divergent thinking in children with Attention Deficit Disorder with Hyperactivity (ADD-H). Divergent thinking is characterized by flexibility of approach to problem-solving and the generation of alternate solutions. 2) to compare the dose-response effects of methylphenidate on divergent thinking with those on attention and on paired associate learning in ADD-H children. 3) to compare unmedicated ADD-H children with normals on tests of paired associate learning and divergent thinking. Twenty children between 6 and 12 years of age diagnosed as having ADD-H (DSM III) will be identified. Each child will be assessed on 6 occasions, each separated by a week: 3 drug days varying in dosage (low, .3mg/kg; medium, .6mg/kg; high, 1.0 mg/kg) and 3 placebo days. The first day will be a placebo day for all subjects; the second and third placebo days will be randomly interspersed among the second through sixth days. Tests administered, beginning 1 1/4 hours following drug or placebo, will be: the Wallach-Kogan Tests (W-K Tests) of divergent thinking; the Paired Associate Learning Test PAL;/the Children's Checking Task (a measure of attention). In addition, the performance of ADD-H children on the first placebo day on the W-K Tests and on the PAL will be compared with that of a matched sample of twenty normal controls. The effects of stimulant medication on higher order cognitive functions in ADD-H children have not been systematically investigated. Clinical observations and data from animal studies suggest the possibility that stimulants may produce cognitive constriction and rigidity which, while enhancing performance on the highly structured routinized tasks/used to assess attention in the laboratory, may concomitantly hamper performance on tests which call for divergent thinking. Negative drug effects on divergent thinking may help to account for the finding that poor academic performance of ADD-H children is unremediated by long-term stimulant drug treatment and would undoubtedly have implications for future cinical practice. Comparisons between unmedicated ADD-H children and normals will help to characterize the cognitive functioning of ADD-H children and aid in the development of appropriate treatments.